This invention relates generally to lubrication means enabling both metal and/or ceramic bearing structures to resist mechanical wear when utilized in a temperature range extending from about -60.degree. C. up to at least 500.degree. C. and higher, and more particularly to employing an improved source of lubrication as the means for doing so. This invention was also made with Government support under contract F33615-90-C-2086 with the Department of the Air Force. The Government has certain rights in the invention.
Lubrication is a well recognized means to reduce friction and wear between bearing surfaces in dynamic physical contact. As such, a pair of load bearing surfaces having relative movement therebetween will be in rolling or sliding contact, as well as combinations thereof, which can include a wide variety of known structural articles such as journal bearings, piston rings, gears, cams and the like. Two major areas for which improved lubricants are needed for continued progress are metal-forming and transportation. Better metal-forming capabilities to minimize machining and grinding require lubrication techniques and lubricants that can be used effectively at temperatures approaching the melting points of the metals now employed. In transportation, one of the most productive areas for increasing energy efficiencies is often referred to as high temperature engines wherein temperatures range from 300.degree. C. and above making the selection of lubricants and means for lubrication difficult. In other known high temperature engine applications, high bearing contact pressures to 300,000 psi are experienced making lubrication most difficult with existing lubrication systems. A known technique for lubrication at such high operational temperatures and pressures is the use of solid lubricants in the form of plasma sprayed coatings of metals and ceramics being employed.
A more recently discovered vapor-phase means of lubrication enables both metal and ceramic bearings to be operated satisfactorily at elevated temperatures of at least 300.degree. C. and higher. For example, a tenacious polymer lubricating film is disclosed in U.S. Pat. No. 5,139,876 upon treating ceramic bearing surfaces during operation at elevated temperatures of at least 350.degree. C. with vaporized organic reactants such as petroleum hydrocarbon compounds, mineral oils, various synthetic lubricants and to further include tricresyl phosphate (TCP) and triphenyl phosphate. In a still more recently issued U.S. Pat. No. 5,351,786, there is further disclosed lubrication means for such operation of the bearing devices with polymer lubricants formed in-situ upon vapor-phase deposition of various phosphazene compounds. For the vapor-phase lubrication of ceramic bearing devices in such manner, it has also been found that formation of the desired polymer lubricant can possibly be further enhanced by ancillary means. Accordingly, U.S. Pat. No. 5,139,876 discloses formation of the lubricating film after first treating the uncoated ceramic surface at elevated temperatures with activating metal ions comprising a transition metal element selected from the Periodic Table of Elements to include iron and tin. There is similarly disclosed in U.S. Pat. No. 5,163,757 a lubrication means for ceramic devices utilizing metal oxide lubricants formed during bearing operation. As therein disclosed, continuous lubrication of the ceramic bearing surfaces is provided with solid metal oxide lubricants formed in-situ with an oxidizable metal source located in physical proximity to the ceramic bearing surfaces being treated. A representative lubrication system enabling such mode of operation includes (a) support means causing the ceramic bearing surfaces to be maintained in dynamic physical contact, (b) an oxidizable metal source located in physical proximity to the support means, and (c) heating means for continuously heating the metal source while the ceramic bearing surfaces are being operated sufficient to provide the solid metal oxide lubricants. In one embodiment, the ceramic bearing means employs ceramic ball bearings supported within the ceramic race with a metal housing member enclosing the bearing structure. Utilizing oxidizable metal for construction of said housing member, including molybdenum and iron alloys, provides a suitable metal source in sufficient physical proximity to the bearing surfaces for satisfactory lubrication at the aforementioned operating conditions.
On the other hand, various bearing structures required to be operated satisfactorily at extremely low service temperatures, such as -60.degree. C. and below, require lubrication means enabling the lubricant to be initially introduced as a liquid at such temperatures. For example, gas turbine engines, low heat rejection combustion engines and the like now employ bearings requiring lubrication when operated at such low environmental temperatures while further encountering elevated operating temperatures often exceeding 300.degree. C. While synthetic lubricants such as liquid polyalphaolefins (PAO) are known to have service temperature ranges extending from -70.degree. C. up to 200.degree. C., none are found to undergo vapor-phase polymerization in order to experience the superior lubrication provided thereby at elevated temperature bearing operation.
It remains desirable, therefore, to provide lubrication of both metal and ceramic bearing means when utilized over a wider temperature range under various atmospheric conditions by still more effective means.
It is another object of the present invention to provide means for continuous lubrication of metal and ceramic bearing surfaces with a novel class of vapor-phase deposited polymer lubricants formed in-situ.
A still further object of the present invention is to provide a novel method for lubrication of metal and/or ceramic bearing surfaces at relatively low lubricant levels with vapor-phase deposited lubricants.
These and further objects of the present invention will become more apparent upon considering the following detailed description of the present invention.